a 427 and 460 are easy to tell apart, but the 427, 390 and 352 all look alike, with narrow heads, wide intake and 5 bolt valve covers...
where as the 429/460 have wide heads, narrow intake, and 7 bolt valve covers.
427's never really came in Mustangs, just special ordered Shelbys, from 68 to 70 you could get a 390 or 428, and from 70 -73 a 429, but no 460 was ever offered in a Mustang..
only the Shelbys had serial numbered blocks, all the Mustangs just have casting codes and restorers use these date codes to determine if it's original to the car, so they can be replaced, but have to match the casting code date and line..
1965-1970 Mustang Codes
Code 64-1/2 65 66 67 68 69 70 -A Raven Raven Raven Raven Raven Raven Raven Black ... Transmission Codes ... Engine Codes ...
Decoding Ford casting part numbers
Ford and Mustang Intake manifold. 4V, 2x4v, 3x2v, Ford Mustang Mercury Tunderbird Galaxie Torino Fairlane Cougar Eliminator Boss Cobra Jet Tunderbolt and Shelby.
Guide to Decoding Ford Part Numbers - ClassicMustang.com
Those are those big long codes (C7ZZ-6540544-DR, etc) that ... Many Mustang parts were originally designed for the Falcon and carry a Falcon casting number. ...
The Mustang Shop - How to read Ford casting numbers
TMS - The Mustang Shop! Parts, performance, restoration, service, information ... Casting numbers are those big long codes (C7ZZ-7528-H etc) that you will find on ...